How does the cspa work?

there are various things that have to be taken into consideration. but one of the most important ones is how long it took the petitioner and applicant to initiate action on getting a visa after it became available. they must take action within one year to preserve eligibility under the CSPA, which these days is taken to mean responding to the notification by the National Visa Center. So, if the petition was approved while the child was under 21, but they were interviewed afterwards, they'd still be eligible unless the family was late in getting the process started. In reality few of the children in the 17-18 age range would lose eligibility for F2a status under CSPA. It's not uncommon now for adults in their mid-20s to retain eligibility under the CSPA, unless they married at some point.